1. Field of Invention
The present invention relates to an excimer lamp comprising a discharge vessel made of silica glass having a discharge space, wherein a pair of electrodes is provided on both sides of the silica glass vessel and wherein excimer discharge is generated inside the discharge vessel.
2. Description of Related Art
Various technologies have been developed and put into practical use recently for treating an article made of metal, glass or other materials by means of the action of vacuum ultraviolet radiation with a wavelength of at most 200 nm and ozone generated thereby by radiating the vacuum ultraviolet radiation onto the article to be treated, which includes a cleaning treatment technology for removing organic impurities adhering to the surface of the article and an oxide film formation treatment technology for forming an oxide film on the surface of the article to be treated.
As an example, a device for emitting vacuum ultraviolet radiation is equipped with an excimer lamp as a light source in order to form excimer molecules by means of excimer discharge and uses the radiation emitted from the excimer molecules. Many efforts have been made in order to enhance the intensity of ultraviolet radiation emitted from such an excimer lamp with greater efficiency.
Specifically, as shown in FIGS. 4(a) & 4(b), an excimer lamp 50 comprising a discharge vessel made of silica glass, which allows passage of ultraviolet radiation, is described, wherein electrodes 55, 56 are provided on the inner side and outer side of the discharge vessel 51 and wherein ultraviolet reflection films are formed on the surfaces exposed to a discharge space S of the discharge vessel 51. An ultraviolet reflection film made only of silica particles and that made only of alumina particles are described as examples in embodiments (See Japanese Patent Publication JP 3580233 B2).
This excimer lamp is provided on part of the discharge vessel 51 with a light exit part 58 from which ultraviolet radiation generated in the discharge space S can exit because the ultraviolet reflection film 20 is not formed on this part.
It is described that an ultraviolet reflection film is provided on the surface exposed to the discharge space S of the discharge vessel 51 in an excimer lamp having the aforementioned configuration, ultraviolet radiation generated inside the discharge space S is reflected by the ultraviolet reflection film, and therefore, does not enter the silica glass in this area in which the ultraviolet reflection film is provided, and ultraviolet radiation passes through the area provided with the light exit 58 to be emitted to the outside, which basically allows effective use of ultraviolet radiation generated inside the discharge space S. Moreover, damage caused by ultraviolet distortion on the silica glass provided in the area other than the light exit part 58 can be minimized, thus preventing the generation of cracks.
However, it was found that there was a problem in excimer lamps equipped with the aforementioned ultraviolet reflection film that the illuminance becomes uneven in the axial direction of the discharge vessel.